Technical notes about Anti aliasing differential filter- november 2014

R. Assiro - P.Creti

Differential Anti-alias filter

Differential Anti-alias filter

x5

x1X1.2

X6

Low G

High G

ADCInput signal

PMT Single channel front-end

Input of second stage is fixed to 100 ohmsThe filter is calculed by elsie 2.72 program with 20 ohm input impedanceThe maximum filter attenuation is -2dB

First stage Second stage-2dBOn filter

R. Assiro - P.Creti

Filter simulated

Filter tested

Output  of twin channels (high gain and low gain) on sweep of frequency(input signal -30dBm)

Cutoff 60 MHz

R. Assiro - P. Creti

Front end type 1

100 ohm input impedanceof second stage amplifier

Low gain0dB

high gain30dB

20

20

20

20

10p

33p 51p 75p

20N

20N 43N 100N

100N

43N

10p

20N

20N 43N

100N

100N

75p51p33p

100N

GND150

GND

150

100 ohm already present

To obtain the same filter, and the same answer, we must correct the valueof the input impedance of second stage of the low gain channel.The high gain channel already has the impedance to 100 ohm

R. Assiro - P. Creti